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Sidewalk replacement contributes to Minneapolis tree loss

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sidewalk.jpgLast June a windstorm toppled about 1,800 trees in Minneapolis. Many of the fallen trees were in boulevards (the area between sidewalks and streets) rather than in yards. This raised concerns that recent sidewalk replacement—and resulting severed tree roots—had been a factor.

To better understand the higher-than-normal losses, the Minneapolis Park and Recreation Board (MPRB) turned to the U’s Urban Forestry Outreach, Research and Extension lab. “The MPRB Forestry Department has partnered with the University of Minnesota for years,” says Ralph Sievert, MPRB forestry director. “When this study presented itself, we did not hesitate to ask the lab to participate.”

Led by forestry department professor Gary Johnson, the lab studied damaged and undamaged trees along the storm’s path. The data set included 3,076 trees, of which 367 were total failures (tipped or partially tipped) due to the storm.

“The major finding is that replacing the sidewalk increased the odds of root failure by 2.24 times,” Johnson says. For example, when no replacement work was done, the average linden had a 10.6 percent chance of root failure; with sidewalk replacement, this increased to 21.0 percent.

When combined with replacement work, tree species was also a significant factor. Linden trees were most likely to fail, followed by ash, maple, and elm. “Essentially, when replacement work was done near any one of these trees, the rate of failures more than doubled,” Johnson says.

“Now we have a great opportunity to make improvements,” Sievert says. “I’m anticipating this leading to safer, healthier trees with fewer instances of infrastructure damage.”

Read the full article in the June issue of Catalyst.

New bridge technology featured at demo in Luverne

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GRS.jpgIt’s an unlikely spot for a fancy new bridge. But the farmers who’ve been driving a two-mile detour for the past 20 years are quite pleased. Smack in the middle of the farm fields and prairie that blanket windy Rock County just east of Luverne in the far southwestern corner of Minnesota, you can find the state’s first Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS).

The Federal Highway Administration (FHWA) teamed up with MnDOT and Rock County to build the bridge between snowstorms this past spring as a way to introduce the technology to wary public works officials in the state and to conduct further testing. A daylong showcase event in June, which included a tour of the project site, drew around 40 participants from five states, mostly engineers. The event was the third demo nationally of GRS-IBS as part of the FHWA’s Every Day Counts initiative.

The method uses alternating layers of granular fill and sheets of geotextile reinforcement.

There are now more than 100 of these bridge systems around the country. The GRS-IBS technology uses alternating layers of compacted granular fill material and fabric sheets of geotextile reinforcement to provide support for the bridge instead of conventional supports. The simple construction method can lower costs, slash construction time, improve durability, and increase worker safety.

“We’ve always had this location on our list of projects to do, but we never had the funding to do it,” said Rock County Engineer Mark Sehr. “With the assistance of Federal Highway and the Minnesota DOT, we were able to fund this project and, therefore, we’ll get one of our roadways open that’s been closed for a number of years.”

And if everything works out as planned, there’ll be no bump between the bridge and approaching roadway caused by uneven settlement. Eliminating that characteristic of conventional bridge systems is a key feature of the new technology.

Watch video highlights of the demo


Imagine replacing the derivatives of crude oil needed to produce conventional asphalt with renewable, cost-competitive, regionally produced, and high-performing materials derived from non-food biomass such as switchgrass, hybrid poplar, or cornstover. The idea portends a whole new world of possibilities and likely could stand the traditional petroleum-based economy on its head.

Researchers at Iowa State University are doing just that, producing bio-oil and bio-char through a process called fast pyrolysis. New bio-oil fractionation technologies also developed at ISU separate the bio-oil into different fractions—some of which appear to be ideal materials for asphalt.

In addition to developing thermoplastic elastomers (polymers) from vegetable oils—which offer many transportation-related applications—ISU researchers are examining and exploring the "bioeconomy," from all phases of the production process to product development and diversification opportunities.

Such collaborative opportunities involving transportation and the bioeconomy were featured during a half-day TERRA Innovation Series event in August at Iowa State University in Ames, Iowa.

A bioeconomy makes use of biorenewable resources, including biomass, for the production of chemicals, fuels, materials, and energy to sustain economic growth and prosperity. Iowa State's bioeconomy research is cross-disciplinary and includes research groups from the areas of agriculture, plant sciences, agricultural engineering, agricultural economics, mechanical engineering, chemical and biological engineering, civil engineering, and numerous others.

Read the full article in the October issue of TERRA E-News.

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Center for Transportation Studies

University of Minnesota

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Minneapolis, MN 55455

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